6/12 roof pitch in degrees
A 6/12 roof pitch is 26.5651°. That is a 50.00% grade, a slope ratio of 1 : 2, and a rafter factor of 1.118034, and the angle is irrational so it carries the ≈.
Change the pitch
26.5651°≈
Multiply your run by 1.118034 for the rafter length. The cuts and the birdsmouth are in the app.
Rafter length at 6/12, by span
Run is half the span on a symmetrical gable. Length is along the rafter, before any birdsmouth, ridge or tail is taken off.
| Building span | Run | Rafter length | Decimal feet |
|---|---|---|---|
| 20 ft | 10 ft | 11' 2-3/16" | 11.180 ft |
| 24 ft | 12 ft | 13' 5" | 13.416 ft |
| 28 ft | 14 ft | 15' 7-13/16" | 15.652 ft |
| 32 ft | 16 ft | 17' 10-11/16" | 17.889 ft |
| 36 ft | 18 ft | 20' 1-1/2" | 20.125 ft |
Every row is the run multiplied by 1.118034, the rafter factor for 6/12. The same figure for every pitch is on the full roof pitch chart.
What 6/12 means on the roof
Six in twelve is the most common residential roof pitch in the United States, and it is usually taken as the top of what is comfortably walkable. Past here most roofers start reaching for jacks.
The working is the arctangent of the rise over the run: atan(6 ÷ 12) = 26.5651°. The rafter factor is the hypotenuse of the same triangle over its base, √(12² + 6²) ÷ 12, which is why multiplying any run by 1.118034 gives the rafter. That figure is the roof pitch multiplier, and it is the same number whatever the size of the roof.
Shingle slope limits quoted here are from the IRC, the United States model code. Your state, province or county may amend them, and several do.